Pathogenesis of Newcastle disease in chickens experimentally infected with viruses of different virulence

Groups of 4-week-old White Rock chickens were inoculated intraconjunctivally with nine isolates of Newcastle disease virus representing all pathotypes. Birds were monitored clinically and euthanatized sequentially, with collection of tissues for histopathologic examination and in situ hybridization using an anti-sense digoxigenin-labeled riboprobe corresponding to the sequence of the gene coding for the matrix protein. Disease was most severe with velogenic viscerotropic pathotypes and was characterized by acute systemic illness with extensive necrosis of lymphoid areas in the spleen and intestine. Viral nucleic acid was detected in multiple tissues but most prominently in macrophages associated with lymphoid tissue. Velogenic neurotropic isolates caused central nervous system disease despite minimal amounts of viral nucleic acid detected in neural tissue. Mesogenic and lentogenic pathotypes caused no overt disease; however, viral nucleic acid was present in myocardium and air sac epithelium following infection with these isolates. Compromise of air sac and myocardium may predispose mesogen- and lentogen-infected chickens to secondary infection and/or decreased meat and egg production.     

Lesions in lambs experimentally infected with bovine respiratory syncytial virus

Respiratory syncytial virus was inoculated intratracheally into five 1-week-old lambs. Three of the lambs responded clinically with fever, hyperpnea, and listlessness. Pulmonary lesions consisted of multifocal areas of consolidation, with necrosis of individual epithelial cells of the airways and accumulation of necrotic debris, macrophages, and few neutrophils in terminal airways and alveoli. Pulmonary septa in affected areas were infiltrated with numerous macrophages and lymphocytes. Viral particles were seen as buds on epithelial cells and free in bronchioles and alveoli.     

Newcastle disease virus pathogenesis in the respiratory tract of local or systemic immunized chickens.

Establishment of selective immunity, local or systemic, made it possible to evaluate the pathogenesis of Newcastle disease virus (NDV) in the respiratory tract of chickens that were previously immunized with beta-propiolactone-inactivated antigen. NDV was inoculated intranasally or intramuscularly to chickens in different states of immunity (local or systemic). Humoral antibodies protected chickens against intranasal as well as intramuscular infection. Local antibodies, on the other hand, conferred immunity only against intranasal challenge. The respiratory tract supported multiplication of the virus, producing a self-limited subclinical infection. Replication of the virus in this system was negligible, playing only a minor role in the pathogenesis of the disease.     

Pathogenesis of chicken-passaged Newcastle disease viruses isolated from chickens and wild and exotic birds

The pathogenesis of six Newcastle disease virus (NDV) isolates recovered from chickens (Ckn-LBM and Ckn-Australia) and wild (Anhinga) and exotic (YN parrot, pheasant, and dove) birds was examined after the isolates had been passaged four times in domestic chickens. Groups of 10 4-wk-old specific-pathogen-free white leghorn chickens were inoculated intraconjunctivally with each one of the isolates. The infected birds were observed for clinical disease and were euthanatized and sampled at selected times from 12 hr to 14 days postinoculation or at death. Tissues were examined by histopathology, by immunohistochemistry (IHC) to detect viral nucleoprotein (IHC/NP), and by in situ hybridization to detect viral mRNA and were double labeled for apoptosis (terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling ([TUNEL] or IHC/caspase-3) and viral nucleoprorein (IHC/NP). Birds infected with the three low virulence viruses (Ckn-LBM, YN parrot, and Ckn-Australia) did not develop clinical disease. Microscopic lesions were observed only at the inoculation site and in organs of the respiratory system. The detection of viral nucleoprotein (N) was restricted to the inoculation site. The pheasant and dove isolates were highly virulent for chickens with marked tropism for lymphoid tissues, confirmed by the presence of large numbers of cells positive for viral N protein and viral mRNA. Viral N protein was detected early in the cytoplasm of cells in the center of the splenic ellipsoids. The apoptosis assays (TUNEL and IHC/caspase-3) showed increased apoptosis in the splenic ellipsoids as well. Apparently, apoptosis is an important mechanism in lymphoid depletion during NDV infection.     

Ultrastructural pathology of the upper respiratory tract of rabbits experimentally infected with Pasteurella multocida A:3.

Twenty-four 8 to 9 week-old Pasteurella multocida -free rabbits were divided into three equal groups, the first group was pretreated with hydrocortisone and inoculated intranasally with pasteurella multocida serotype A:3. The second group was inoculated intranasally with P. multocida without hydrocortisone treatment. The third group was inoculated with phosphate buffered saline only and used as a control group. Pasteurella multocida was isolated from the nasal cavity of all infected rabbits in group 1 and 2 and from the trachea of seven rabbits in group 1 and five rabbits in group 2. This study was conducted to observe the ultrastructural changes of the upper respiratory tract of hydrocortisone treated and non-treated rabbits infected with P. multocida serotype A:3. The ultrastructural changes detected in infected rabbits were ciliary destruction and deciliation of the ciliated epithelial cells, cellular swelling, goblet cell hyperplasia and endothelial cell damage. Pasteurella multocida was observed attached to the degenerated cilia, microvilli and mucus. Pasteurella multocida infection was associated with inflammatory responses, which may have caused tissue damage. It is possible that hydrocortisone modulates the severity of infection as an immune suppressor and an inhibitor of goblet cell secretion.     

Protein concentrations and immunosuppressive properties of serum in chickens experimentally infected with avian tumor viruses

Sera from chickens affected by Marek's disease or developing Rous sarcoma were investigated. There were changes in the protein fractions, and the amount of alpha and beta fractions was consistently increased. At the same time, immunosuppressive factors were found to inhibit the number of plaque-forming cells in the spleen of mice immunized with sheep red blood cells.     

Characterisation of Newcastle disease viruses isolated in India.

Eleven Newcastle disease virus (NDV) isolates obtained from outbreaks of disease in chickens (9) and Japanese quail (2) in Tamil Nadu, India were characterised in pathogenicity tests, antigenically, using mouse monoclonal antibodies (MAbs), and other established tests devised to distinguish between different strains. All 11 isolates were shown to be highly virulent for chickens. In indirect immunoperoxidase tests used to assess the ability of a panel of 28 MAbs to bind to infected cell cultures, 10 of the isolates showed an identical reaction pattern, the other isolate (No. 4) failed to react with one MAb which bound to cells infected with the other isolates. Isolates 9 was unstable at pH 3 while the other 10 were stable. All other properties were shared by the 11 isolates.     

Pathological changes of tracheal mucosa in chickens infected with lentogenic Newcastle disease virus

Forty-day-old specific-pathogen-free chickens were exposed by aerosol to lentogenic Newcastle disease virus (NDV) and observed for 24 days for pathological changes in the tracheal mucociliary system. Specific fluorescence of NDV antigen was observed through day 5 postexposure (PE) in the cytoplasm of the tracheal epithelium and desquamated epithelium in the lumen. On day 1 PE, scanning electron microscopy revealed hypertrophy of goblet cells and small patches of the deciliated epithelium scattered mainly around the openings of mucous glands. The deciliated area of tracheal surface increased through day 4 PE. Light microscopy showed small vacuoles containing lymphocytes and heterophils in the epithelial layer. Immature epithelium proliferated in some areas. On days 5 and 6 PE, ciliated areas of the trachea tended to increase as a result of regeneration of the epithelium, still leaving many nonciliated patches of various sizes. On and after day 8 PE, there remained plaques with nonciliated flat epithelium, but most areas were covered with well-ciliated epithelium. Non-ciliated plaques were observed until day 24 PE, but they gradually decreased in size. These plaques were covered by a single layer of flat epithelium and were formed upon lymph follicles in subepithelial tissue.     

Vaccinia viruses isolated from skin infection in horses produced cutaneous and systemic disease in experimentally infected rabbits

The susceptibility of rabbits to two isolates of Vaccinia virus (VACV) recovered from cutaneous disease in horses in Southern Brazil was investigated. Rabbits were inoculated in the ear skin with both VACV isolates, either in single or mixed infection. All inoculated animals presented local skin lesions characterized by hyperaemia, papules, vesicles, pustules and ulcers. Infectious virus was detected in the lungs and intestine of rabbits that died during acute disease. Histological examination of the skin revealed changes characteristic of those associated with members of the genus Orthopoxvirus. These results demonstrate that rabbits develop skin disease accompanied by systemic signs upon intradermal inoculation of these two equine VACV isolates, either alone or in combination, opening the way for using rabbits to study selected aspects of the biology and pathogenesis of VACV infection.     

Two types of Newcastle disease viruses isolated from feral birds in Western Australia detected by monoclonal antibodies

Thirteen viruses isolated from feral birds and one isolated from a domestic duck, obtained in 1979-1980 during a survey of birds in Western Australia, were shown to be Newcastle disease viruses of low virulence for chickens. The binding of mouse monoclonal antibodies, raised against NDV-Ulster 2C to MDBK cells infected with the isolates was assessed using an indirect immunoperoxidase test. Five viruses caused binding of all 9 monoclonal antibodies tested, whereas the other 9 isolates induced binding of only 4 monoclonal antibodies.